The present invention relates to a process for treating a flue gas, and more particularly to a process for removing dust and sulfur oxides from a gas containing dust and sulfur oxides, which may be hereinafter referred to merely as "SO.sub.x ", such as coal combustion flue gas, etc.
Flue gas from combustion of coal, petroleum, etc. usually contains a few 100 to a few 1,000 ppm of SO.sub.x. Since SO.sub.x is an air pollutant, various processes for abating discharge of SO.sub.x to the surrounding atmosphere have been developed and practically used. Typical processes for treating SO.sub.x include a limestone-gypsum process comprising absorbing SO.sub.x in calcium carbonate slurry, oxidizing the slurry, thereby converting the slurry to gypsum, and recovering the gypsum, a process of absorbing SO.sub.x in an aqueous alkaline solution of caustic soda, caustic potash, etc., a process of using an adsorbent such as activated carbon, copper oxide, etc., as disclosed in Chem. Eng. Progress Vol. 51, No. 5, May (1975) pages 66-71. Among these processes, the limestone-gypsum process is most widely used for treating a large volume of a flue gas such as boiler flue gas of power plants. However, the limestone-gypsum process and the process of using an aqueous alkaline solution of caustic soda, caustic potash, etc. require waste liquor treatment, and the process of using an adsorbent requires regeneration of the adsorbent after the adsorption of SO.sub.x. In addition to these problems, the limestone-gypsum process requires heating of flue gas after the removal of SO.sub.x, because the temperature of the flue gas is lowered at the removal of SO.sub.x, and the process of using the aqueous solution of caustic soda, caustic potash, etc. requires a large amount of the reagent.